1. Field of the Invention
The present invention relates to a constant-speed cruising system for a vehicle, adapted to automatically control a vehicle speed governing mechanism of an engine so as to reach a target vehicle speed set by the driver.
2. Discussion of the Related Art
For the engine of an Otto type, for example, it is common that a constant-speed cruising system for the vehicle is designed to subject a vehicle speed governing mechanism such as a throttle valve and so on to feedback control on the basis of output from a vehicle speed detecting means for detecting an actual vehicle speed.
Japanese Utility Model Examined Publication (Kokoku) No. 10,361/1984 discloses a constant-speed cruising system in which a microcomputer is used as a control unit for constant-speed cruising control. This constant-speed cruising system has a set switch and a cancel switch as instruction signal outputting means to be outputted to the control unit. The set switch has the function to set an actual vehicle speed to a target vehicle speed for constant-speed cruising control at the time when the driver has turned the set switch on. The cancel switch may include, for example, a brake switch and so on, which is disposed on a foot brake pedal, and it is designed such that the brake switch is turned on as the foot brake pedal is stepped down, thereby releasing the constant-speed cruising control.
It is further disclosed in the above-mentioned publication that a clutch interposed between the throttle valve and an actuator is turned on to connect the throttle valve to the actuator when the constant-speed cruising control is implemented and the clutch is turned off to disconnect the throttle valve from the actuator during no implementation of the the constant-speed cruising control. The clutch is provided with a clutch control circuit for its exclusive use in order to turn it on or off. The instruction signal for turning the clutch on or off is generated from the control unit to the clutch control circuit. The instruction signal for turning the clutch off is generated directly to the clutch control circuit from the cancel switch, and the clutch control circuit turns the clutch off immediately in response to the instruction signal from the cancel switch.